The present invention relates to panel fasteners and, more particularly, to a panel fastener having a composite turning knob for use in the electronics field to install electronic equipment into equipment racks and the like. A panel fastener simplifies the installation or removal of the equipment from the racks.
Racks for mounting electronic equipment usually are organized into bays having frames to hold the equipment. The frames of each bay typically have predrilled holes spaced apart at standard distances. The electronic equipment is of a standard size designed to fit in the frames and has holes designed to align with the corresponding holes in the frames. A threaded fastener is used to secure the equipment to the frame.
Installing electronic equipment into a frame can be difficult since a technician must simultaneously hold the equipment, align the holes and thread the fastener into a corresponding threaded hole. In addition, the technician must hold the fastener substantially perpendicular to the threaded hole and must apply a small amount of insertion force to insert a threaded stud of the fastener into the threaded hole, while simultaneously rotating the stud.
To overcome the difficulties encountered with conventional threaded fasteners, so-called panel fasteners have been developed to simplify the equipment installation process. The panel fastener has a turning knob that allows for easy handling and tightening of the fastener with the fingers. A conventional panel fastener has a threaded stud or screw, a spring, a sleeve and a turning knob to allow the fastener to be inserted and tightened by hand. Thus, a piece of equipment is installed in an equipment rack by positioning the threaded portion of the shaft through a threaded hole in the equipment rack's frame and tightening the fastener by pressing the knob inward, compressing the spring, and rotating the knob to engage the threaded hole. The top of the knob is open, leaving the stud head exposed to allow final tightening by a screwdriver, if desired. The spring keeps a continuous withdrawal force on the fastener stud to facilitate removal of the panel fastener.
In panel fasteners of the type described above, the knob usually is made of aluminum and the stud or screw is made of steel. The circumference of the stud head also has a serrated or knurled outer surface with an outside diameter slightly larger than the inside diameter of the cylindrical aluminum knob. To assemble the fastener, the steel stud is inserted axially into the knob, causing the serrations or knurling on the stud head to frictionally engage the inner surface of the knob. Rotation between the stud head and the knob therefore is prevented primarily by the interference fit, and corresponding frictional engagement, created by the serrations or knurling, between the steel stud head and the softer aluminum knob. The aluminum knob is then swaged over the top outside edge of the stud head to prevent axial movement of the stud with respect to the knob.
Since the aluminum knob and the steel stud are made of dissimilar materials, there is a tendency for corrosion to occur between the two metals in certain environments. In addition, there is a tendency for the knob to crack when pressed and swaged over the stud since the stud head has an outside diameter that is slightly larger than the inside diameter of the knob. Another disadvantage of the prior panel fasteners is the inability of the interference fit to positively prevent rotation between the stud head and the knob when a large rotational torque is applied to the knob. In this regard, once the knob is rotated with respect to the stud head, the softer aluminum knob is damaged and the interference fit and frictional engagement between the stud head and knob is effectively destroyed. The knob will then rotate on the stud head when tightening forces are applied, and most of the advantages of the panel fastener are lost unless the entire panel fastener assembly is replaced. Also, if the knob is broken off of the stud, the stud is no longer captured in the assembly and can be forced out of the assembly by the spring.
Accordingly, there has existed a definite need for a panel fastener having a turning knob that has a positive locking engagement with the stud head, that is corrosion resistant, and that avoids cracking during assembly. There also has existed a need for a panel fastener in which the stud remains captured in the remaining assembly if the knob is broken off of the stud. The present invention satisfies these needs and provides further related advantages.